Even today, over 100 years after its release, you can’t call yourself a film buff if you haven’t seen “The Birth of a Nation.”

Yes, it is overtly racist with scenes to make all but the most virulent white supremacist cringe. But it also is the origin story of cinema itself, the motion picture as Ur text, the one that introduced the language of film. The shots, editing and storytelling techniques that director David Wark Griffith pioneered and that remain the foundations of how you tell a story with moving pictures.

But “Birth” isn’t just the starting point for modern film history. It gave birth to two movements on opposite sides of America’s racial schism. The movie revived the defunct, racist minority-oppressing Ku Klux Klan, brought it out into the open and set the stage for another half century of Jim Crow laws and lynchings. And protesting the movie unified Black America like nothing before it, setting the mission of the NAACP in stone and predicting the organized protests of the Civil Rights movement which began just over thirty years after the film became the cinema’s first blockbuster.

“Birth of a Movement: The Battle Against America’s First Blockbuster,” wonderfully sketches in the history leading up to the film’s 1915 release, its artistry and malign racial politics, and then tracks its impact, both as “inspiration” and justification for the spread of Jim Crow racial discrimination laws and the protests — “direct action” — that erupted as well.

It’s a documentary that provides “context,” as Spike Lee puts it, recalling the first time he was exposed to the movie at film school at NYU. Context was long missing from this movie, as it popped up in history of film classes, revival screenings and the like.

Filmmakers Bestor Cram and Susan Gray provide that, and history we’ve forgotten in their concise, smart and thorough film. Historians like Henry Louis Gates, film scholars from here and abroad, social scientists and filmmakers like Lee and Reginald Hudlin detail the film’s place in cinema lore, its problems and a hero who emerged from the battle over the movie in 1915 Boston.

The hero is crusading newspaperman William Monroe Trotter, whose Boston “Guardian” led the charge to get the film censored and suppressed. It was a hopeless cause, but a righteous one, spitting into the wind of long lines at the nation’s box offices (Blacks could not get tickets in many cities) and the endorsement of President Woodrow Wilson, who called the “Klan saves The South and the Nation from Miscegenation” drama “history written with lightning.”

A little-seen 1930 interview with director Griffith, and footage from the many movies he made leading up to “Birth” is sampled. The racist cinema that predated his masterpiece, short stereotype-building pictures by other filmmakers, is shown.

Most importantly, though, is that context, the flux that the nascent NAACP and state of “Black Leadership” was in before the film’s arrival, the larger conflict that pitted Trotter, his Harvard classmate W.E.B. Dubois against civil rights appeaser Booker T. Washington, before “Birth,” their unity in vilifying the movie after its release.

Scholars like Griffith chronicler Ira Gallen and Vincent Brown make the case that the movie still has value, as a “masterpiece,” as “the first film to have the word ‘propaganda’ attached to it,” and as “historically inaccurate, but an honest distillation of American racial thought at that time.”

I particularly enjoyed Gallen’s setting the record straight about Griffith’s real background (“white trash, poor”) and his romanticized view of that childhood and the racist myth-building he fostered through his sepia toned glasses.

With “Birth of a Movement” PBS has financed an essential cornerstone of any film “History of Film” high school or college course, one that you don’t have to go to class to absorb. It’s right here on Netflix right now.